1. Field of the Invention
This invention relates to a needle bar thread guide which can readily set a needle thread on a threading portion of a thread guide body provided on a lower end of a needle bar in a sewing machine and prevent the needle thread set on the threading portion from falling off.
2. Description of the Related Art
Many conventional sewing machines have been provided with a needle bar thread guide mounted on a lower end of a needle bar of a sewing machine for guiding a needle thread set on a thread take-up lever along the needle bar to a thread eye of a sewing needle. When the needle thread is set on the needle bar thread guide before sewing, the needle thread can be prevented from uselessly swinging near the lower end of the needle bar in vertical movement of the needle bar during sewing.
Various types of needle bar thread guides have been suggested. For example, JP-B-S58-35720 discloses an overlock sewing machine includes a first threading portion formed so as to be opened in one direction and a second threading portion provided below the first threading portion and formed into the shape of a continuous ring, both portions being provided on the lower end of the needle bar. In the disclosed construction, before being passed through the thread eye of the sewing needle, the needle thread is set on the first threading portion and then on the second threading position from above. As a result, the needle thread can be limited to a position near the sewing needle, whereby the needle bar can be prevented from swinging during sewing.
Furthermore, JP-A-11-489 discloses another sewing machine includes a thread guide device having provided over a needle connecting member and having a slit formed so as to be open in one direction. The disclosed sewing machine further includes a needle bar thread guide disposed below the thread guide device and the needle connecting member and formed so as to be open in one direction. The sewing machine is constructed so that the needle thread can readily be set both on the slits and on the needle bar thread guide.
In the sewing machine disclosed in JP-B-S58-35720, however, the second threading portion is formed into a continuous ring shape. Accordingly, the needle thread is passed from above so that the second threading portion is threaded. This renders the threading work troublesome.
Furthermore, in the sewing machine disclosed in JP-A-11-489, each of the thread guide device and needle bar thread guide both disposed over the needle connecting member is formed so as to be open in one direction. Accordingly, for example, the needle thread swings hard when a firm thread such as nylon thread is used for the sewing. In such a case, the needle thread easily falls off from the thread guide device and/or needle bar thread guide when swinging hard.
In view of the above-noted problem, it is expected to devise shapes of components of the needle bar thread guide so that the needle thread can readily be set on and can be prevented from falling off. However, in order that the above-noted mutually contradictory functions may be compatible with each other, it is supposed that the shapes of components of the needle bar thread guide would be complicated considerably. When the shapes of components of the needle bar thread guide become complicated considerably, the components are necessitated to be in high precision and accordingly, the costs of the components are increased.
Furthermore, it would be considerably difficult to reliably prevent the needle thread from falling off only by devices in the shapes of components of the needle bar thread guide. When the needle thread disengages the threading portion of the needle bar thread guide during sewing, the sewing operation becomes unstable and the quality of sewn products would be reduced. Furthermore, there is a possibility of occurrence of thread breakage in a needle thread.